Micromechanical component having a volume-elastic medium

ABSTRACT

A method for manufacturing a micromechanical component is described, the micromechanical component having a medium. The medium has settable and changeable volume-elastic properties and generally completely encloses a sensor module and/or a module housing. The medium preferably has a low-pass response.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/270,087 filed on Nov. 13, 2008 now U.S. Pat. No. 8,148,187, whichclaims priority to German Patent Application No. 10 2007 057 441.1 filedNov. 29, 2007, all of which are incorporated herein by reference intheir entirety.

CROSS REFERENCE

The present application claims the benefit under 35 U.S.C. §119 ofGerman Patent No. 102007057441.1 filed on Nov. 29, 2007, which isexpressly incorporated herein by reference in its entirety.

BACKGROUND INFORMATION

The present invention is directed to a micromechanical component.Conventional methods for manufacturing such micromechanical componentsare generally available. For example, a sensor is described in GermanPatent Application No. DE 102 26 258 A1, a sensor element of the sensorbeing protected by a protective layer. However, this sensor has thedisadvantage that the protective layer is only partially provided overthe sensor element. Areas of the sensor element not covered by theprotective layer can therefore be easily damaged.

SUMMARY

A method according to an example embodiment of the present invention formanufacturing a micromechanical component may have the advantage thatprotection of the sensor module, for example, from mechanical stresses,is achieved using the medium, and the sensor module is concurrentlyfastened within the external housing by the medium without additionalmounting steps. In addition, a frequency filter may be formed by themedium, so that generally only selected frequencies reach the sensormodule in the micromechanical component. Complex fastening mechanismswhich fix the sensor module in the external housing and may be damagedduring the service life of the sensor module, for example, may thus alsobe advantageously dispensed with. Furthermore, the medium produces acomprehensive protection of the sensor module from externally actingsubstances, such as conductive and/or etching liquids.

The sensor module and/or the module housing is/are generally completelyenclosed by the medium; however, an access to the sensor module and/orthe module housing may be shaped intentionally through the medium. Suchan access may be provided if the micromechanical element is used as apressure sensor, for example.

A volume-elastic medium may be understood as a foam-like elastomer whichmay change its volume in an elastically reversible way to a largerextent under changing, external mechanical-thermal stresses than compactsealing compounds, for example. For example, the volume of the medium isto be changeable by approximately 5% to 80%, preferably approximately10% to 30% during the manufacturing of the micromechanical component. Ifthe sensor module is enclosed by the medium, the medium thusadditionally advantageously protects the sensor module during asubsequent injection-molding process to produce the external housing.The pressure arising due to the injection-molding method isadvantageously absorbed by the medium and does not result in damage tothe sensor module. In the finished manufactured micromechanicalcomponent, pre-tensioning of the medium is also preferably caused by theenclosure of the medium inside the external housing. This pre-tensionpreferably continues to exist throughout the entire service life of themicromechanical component and thus ensures that the sensor moduleremains permanently enclosed by the medium even in the event of changingambient temperatures. With regard to the volume-elastic medium,reference is made to the volume-compressible medium in German PatentApplication No. DE 10 2004 053 782 A1, which is expressly incorporatedherein by reference in its entirety.

The medium particularly preferably is constructed as a frequency filterthrough the selection of the material properties of the medium and/orthrough the selection of manufacturing parameters during themanufacturing of the micromechanical component. Thus, the transmissionfunction of the micromechanical component may be varied (set)advantageously by special material properties of the medium—for example,its elasticity or its damping properties—and, for example, the selectionof the distance between the sensor module and the external housing orthe module housing to the external housing. For example, a mechanicallow-pass response having a limiting frequency in the range ofapproximately 100 Hz to 2 kHz, for example, may thus be achieved for amicromechanical component. Furthermore, the material properties of themedium may be changed during the manufacturing by an appropriateselection of the manufacturing parameters, so that correspondingfrequencies may thus also be filtered.

The sensor module is preferably fastened by the medium in a modulehousing and/or the module housing is fastened by the medium in theexternal housing. As already noted, additional fasteners for fixing thesensor module in the module housing and/or the module housing in theexternal housing or the sensor module in the external housing may thusadvantageously be dispensed with. In addition, a protection frommechanical and/or thermal-mechanical stresses and/or from externallyacting substances is advantageously provided by the medium for both themodule housing and also the sensor module. If a sensor module is used,which is fastened in the module housing by the medium, the modulehousing being fastened in the external housing by the medium, the sensormodule is therefore protected particularly reliably, because both themodule housing and also the medium are provided as the protection.

The medium preferably includes a first medium and a second medium, thefirst medium and the second medium preferably having different chemicaland/or physical properties. Particularly preferably, the sensor moduleis enclosed in the module housing by the first medium and the modulehousing is enclosed in the external housing by the second medium. Thedifferent functions of the medium (fastening, protection, frequencyfilter) may thus advantageously also be fulfilled by two media havingdifferent chemical and/or physical properties, whereby the functions maybe fulfilled with greater decoupling.

In the context of the present invention, one medium is referred to, evenif this is to be understood to mean a first medium and a second medium.The properties or embodiments of the medium may relate to both the firstmedium and also the second medium or only the first medium or the secondmedium. At least the first medium and/or the second medium is/areprovided as volume-elastic, reference being made to the definitionalready given in regard to the term “volume-elastic.”

The viscosity of the medium preferably rises during the manufacturing ofthe micromechanical component, for example, by chemical cross-linking.The medium preferably changes during the manufacturing of themicromechanical component from a medium having flow properties to amedium having solid properties. Particularly sensitive structures maythus particularly advantageously be prevented from being damaged by themedium during the initial enclosure. Nonetheless, secure fastening ofthe sensor module and/or the module housing is achieved by the solidproperties of the medium. For example, a medium may be used whichinitially has low viscosity flow properties during the embedding and/orenclosure of the sensor module, but then exhibits an increase in theviscosity until it becomes a cross-linked solid. In particulartwo-component or multi-component polymers having an elastomer carrierare preferably to be used as the medium for this purpose. In particularan elastomer foam, for example, made of polyurethane or a so-calledliquid silicone rubber may preferably be used as an elastomer for thispurpose.

The medium is preferably pre-tensioned during the manufacturing of themicromechanical component during or by a preferably subsequent enclosureby the external housing. The micromechanical component, specifically itselectrical supply lines, is under a slight residual pressure due to thepre-tensioning, even in the event of various environmental conditions ofthe micromechanical component. An outward seal of the electrical supplylines is ensured in this way even in the event of differing ambientconditions (in particular temperature changes). A possible liquid entryinto the micromechanical component because of pumping effects may thusadvantageously be generally reliably prevented. The pre-tensioning ofthe medium may particularly preferably be performed in that the mediumhas elements whose volumes change particularly greatly—beyond the volumecompressibility of a solid—in the event of corresponding ambienttemperatures and/or by chemical processes during the manufacturing, forexample. The medium is preferably also reversibly volume-elastic afterthe manufacturing.

Internal, closed-cell bubbles are particularly preferably produced in aprecursor stage of the medium and/or admixed in a precursor stage of themedium as such elements in the manufacturing method. Initially thebubbles are preferably liquid-filled. The bubble count and/or the bubblesize during the manufacturing is/are particularly preferably dimensionedin such a way that the space filled up by the medium inside themicromechanical component is pre-tensioned when the medium is enclosedby the external housing. The bubbles represent small gas springs.Alternatively or additionally, the medium may have elastic, generallyhollow microbeads as such elements. Closed-cell bubbles whose liquid isalready irreversibly vaporized before the admixing in the precursorstage of the medium are particularly preferably used as microbeads.These bubbles generally no longer change their volume after theadmixing. The bubbles are particularly preferably mixed into anelastomer.

The bubbles preferably change as a function of the manufacturingparameters. A change in the bubbles is to be understood as an expansionor a shrinkage of the bubbles. The later pre-tensioning of the mediummay be influenced during the manufacturing process by the count and/orthe size of the bubbles and/or the microbeads. If an elastomer is used,for example, the cross-linking rate of the elastomer may be influencedvia the supplied heat as a manufacturing parameter. The expansion of thebubbles within the elastomer may in turn be intentionally influenced bythe cross-linking rate. It should be clear that the bubbles may notexpand in an elastomer which already has solid properties. Therefore thebubbles preferably initially expand up to a predefined volume before theelastomer cross-links generally completely. Of course, both processesmay also run simultaneously, the bubble expansion being stopped upon acorresponding degree of cross-linking of the elastomer. The expansion ofthe bubbles is additionally a function of the processing temperature,the pressure which acts on the medium during the manufacturing, and/or ahigh-energy irradiation of the medium during the manufacturing. Thebubbles particularly preferably have a liquid during the manufacturing,the liquid vaporizing within the bubbles—for example, at an increase inthe processing temperature—within the bubble envelope. The resulting gasand/or vapor mixture remains within the bubble envelope, by which thebubble is inflated. Therefore the bubbles inflate preferablyirreversibly. After a subsequent enclosure of the sensor module and/orthe module housing by the external housing, advantageously nointermediate spaces and/or cavities thus result between the sensormodule and the module housing and/or the module housing and the externalhousing or the sensor module and the external housing except for thebubbles. Without intermediate spaces and with appropriatepre-tensioning, the penetration of substances (such as liquids) withinthe micromechanical component is prevented, by which the sensor moduleis protected from such substances.

The sensor module is preferably embedded in the medium. Furthermore, themodule housing is preferably embedded in the medium. Of course, it isalso possible that first the sensor module is embedded in the medium,the embedded sensor module is received by the module housing, and thenthe module housing is embedded in the medium, before the embedded modulehousing (having the embedded sensor module) is received by the externalhousing. The medium is advantageously processed particularly simply andcost-effectively by the embedding.

Furthermore, the sensor module enclosed by the medium or the modulehousing enclosed by the medium is preferably extrusion-coated and/orembedded to form the external housing. The formation of the externalhousing by extrusion-coating or embedding is advantageously simple andparticularly cost-effective.

In another preferred specific embodiment, the sensor module or themodule housing (having a medium between the module housing and thesensor module or having the sensor module without a medium) ispositioned in the external housing and then embedded in the medium. Ofcourse, the sensor module may also be positioned inside the modulehousing and subsequently embedded in the medium. The external housing ispreferably manufactured by an injection-molding method before theintroduction of the medium.

In a preferred specific embodiment, the medium at least partially has aprotective layer. The protective layer may preferably be formed from themedium itself and act as a mechanical protection from mechanicalstresses and/or as a repellent barrier against externally actingsubstances, for example. The sensor module is advantageouslyadditionally protected by the protective layer, by which the servicelife of the sensor module may advantageously be increased. Of course,the protective layer may be implemented around both a sensor moduleenclosed by a medium and also around a module housing enclosed by amedium.

The protective layer preferably arises in that the bubbles within themedium generally do not expand in the boundary area of the medium. Themedium is less volume-elastic in the boundary area due to the generallyunexpanded bubbles, because the solid properties of the elastomerpredominate. Expansion of the bubbles in the boundary area may beprevented, for example, in that the elastomer cross-links more rapidlyin the boundary area.

A further example embodiment of the present invention is amicromechanical component, the micromechanical component beingmanufactured according to the method described above. Themicromechanical component has a sensor module and/or module housinggenerally completely enclosed by the medium, the medium having afrequency filtering response. Accordingly, frequencies may beselectively filtered by the properties of the medium, the filter actionof the medium being a function of the material properties and/or theprocessing parameters of the medium. The medium particularly preferablyacts as a low-pass filter.

The medium preferably includes a first medium and a second medium, thefirst medium having different chemical and/or physical properties thanthe second medium. The sensor module is particularly preferablygenerally completely enclosed in the module housing by the first mediumand the module housing is generally completely enclosed in the externalhousing by the second medium. Preferably, only the first medium or thesecond medium acts as a frequency filter and the other medium is usedfor fastening the sensor module or the module housing within theexternal housing.

The medium preferably has bubbles within the micromechanical component.The first medium and/or the second medium particularly preferablyhas/have bubbles.

Furthermore, there are preferably generally no cavities and/orintermediate spaces present due to the medium between the sensor moduleand the module housing and/or between the module housing and theexternal housing or between the sensor module and the external housing.The first medium and/or the second medium thus fills/fill up generallyall intermediate spaces between the sensor module and the module housingand/or between the module housing and the external housing or betweenthe sensor module and the external housing. The sensor module and/or themodule housing may thus advantageously be fixed by the medium in itsposition within the external housing.

The micromechanical component is used, for example, as a pressure sensoror as an acceleration sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are illustrated in thefigures and are explained in greater detail below.

FIG. 1 schematically shows a micromechanical component having a medium.

FIG. 2 schematically shows a micromechanical component without a modulehousing.

FIG. 3 schematically shows a micromechanical component having a medium,the medium having a protective layer.

FIG. 4 schematically shows the medium having bubbles.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 schematically shows a micromechanical component 1,micromechanical component 1 having a sensor module 9, a module housing10, a medium, and an external housing 5. The medium includes a firstmedium 7′ and a second medium 7 in the exemplary embodiment, medium 7,7′ also being referred to in the following description. Sensor module 9has a circuit board 2, a sensor chip 3, and at least one terminal pin 6in the exemplary embodiment. It is possible to contact sensor chip 3using terminal pin 6. First medium 7′ encloses sensor module 9 in theexemplary embodiment, second medium 7 enclosing module housing 10.Generally no free spaces (intermediate spaces) result between modulehousing 10 and external housing 5 or between sensor module 9 and modulehousing 10 due to first and second medium 7′, 7 (with the exception ofbubbles 11 inside medium 7, 7′ if medium 7, 7′ has bubbles). Modulehousing 10 and also sensor module 9 are fixed by medium 7, 7′ withinexternal housing 5. Complex fastening devices are thus not necessary.Because first and second medium 7, 7′ have volume-elastic properties,module housing 10 and/or sensor module 9 is/are protected frommechanical stresses, for example, by medium 7, 7′. For example, sensormodule 9 or module housing 10 may be extrusion-coated to form externalhousing 5, without the arising pressures damaging sensor module 9 ormodule housing 10. Medium 7, 7′ thus acts as a cushion in this case.Medium 7, 7′ is preferably pre-tensioned after being enclosed byexternal housing 5, whereby no intermediate spaces arise between sensormodule 9 and/or the module housing and external housing 5. A pumpingaction is thus prevented, whereby no liquids are sucked into externalhousing 5.

FIG. 2 schematically shows sensor module 9 without module housing 10 inmicromechanical component 1. In this case, sensor module 9 is only heldin external housing 5 by first medium 7′. First medium 7′ isadvantageously sufficient here as protection of sensor module 9 against,for example, mechanical stresses (for example, during theinjection-molding method for manufacturing external housing 5). Onecomponent (module housing 10) fewer is advantageously needed formanufacturing micromechanical component 1, by which the manufacturingprocess may be shortened and simplified, the manufacturing costs may bereduced, and the weight of micromechanical component 1 may be decreased.A plurality of sensor chips 3 may be placed in a composite within theexternal housing 5, for example. In this case, sensor chips 3 may becontacted, for example, by wire bonds and/or via isotropic oranisotropic glued bonds and/or via a flip chip mounting on metalliccontact elements of external housing 5.

FIG. 3 schematically shows micromechanical component 1, first medium 7′in the exemplary embodiment having a protective layer 8 as an envelopeand/or external skin of first medium 7′. Protective layer 8 ispreferably used for increased mechanical protection or as an externalterminus of external housing 5. In this case, it is therefore notnecessary for external housing 5 to completely enclose sensor module 9.Protective layer 8 may preferably additionally be altered during orafter the manufacturing process—for example, chemically and/ormechanically—in such a way that it forms a barrier against etchingand/or conductive substances, for example. Protective layer 8 preferablyarises in that bubbles 11 generally do not expand within protectivelayer 8.

FIG. 4 schematically shows a possible embodiment of first medium 7′.First medium 7′ has bubbles 11 in the exemplary embodiment. The bubblesare preferably added to an elastomer as a further component during themanufacturing of micromechanical component 1, the bubbles beingliquid-filled at this time and having a size of approximately 2 μm to 40μm, particularly preferably approximately 10 μm to 20 μm. The liquidvaporizes within the bubbles by increasing the processing temperature,for example, the resulting vapor or gas remaining inside the bubbles.The bubbles thus inflate generally irreversibly, so that they reach asize of approximately 30 μm to 80 μm, preferably approximately 50 μm.Medium 7, 7′ resulting due to the elastomer and the bubbles isdistinguished by an generally homogeneous bubble size (except in thearea of protective layer 8). The bubble size and the bubble count may beset reproducibly during the manufacturing process. Medium 7, 7′ may thusbe adapted optimally to the functions of medium 7, 7′ by bubbles 11 andthrough the processing and the selection of the elastomer. It istherefore possible to reproduce, set, and vary the volume-elasticproperties of medium 7, 7′ in an advantageous manner. The frequencyfiltering properties of medium 7, 7′ thus also become reproducible andsettable.

What is claimed is:
 1. A micromechanical component, comprising: ahousing; a sensor module positioned in the housing; and a volume-elasticmedium enclosing completely the sensor, the medium having a frequencyfiltering response, and the medium being pre-tensioned.
 2. Themicromechanical component as recited in claim 1, wherein the mediumcomprises a first medium and a second medium, the first medium having atleast one of different chemical properties or different physicalproperties, than the second medium.
 3. The micromechanical component asrecited in claim 2, wherein at least one of the first medium and thesecond medium have bubbles.
 4. The micromechanical component as recitedin claim 1, wherein the medium fills up all intermediate spaces betweenthe sensor module and the external housing in the micromechanicalcomponent.
 5. The micromechanical component as recited in claim 1,wherein the sensor is a pressure sensor.
 6. The micromechanicalcomponent as recited in claim 1, wherein the sensor is an accelerationsensor.
 7. A micromechanical component, comprising: an external housing;a sensor module; a module housing enclosing the sensor module, themodule housing being positioned in the external housing; and avolume-elastic medium completely enclosing the module housing, themedium having a frequency filtering response, and the medium beingpre-tensioned.